Integrated hydrodynamic air bearing and seal
A pressurized hydrodynamic bearing and seal assembly for radial and/or thrust bearings includes a stationary bearing member formed of a carbon/graphite material positioned adjacent a rotating member so as to define a space between the members when the respective bearing segments are rotating with respect to each other. In one form, the carbon/graphite is positioned in the outer stationary position and the inner member is fixed to a rotating shaft. The inner member may be formed of a metallic material or a ceramic or ceramic composite. The operation of the bearing is improved by including a seal dam along an axial end of the stationary carbon/graphite member so as to prevent leakage of gases accumulating between the inner and outer members. In this form, the gas pressure can be increased substantially so as to increase the load capacity of the bearing. The system also includes a thrust bearing of substantially the same type of construction but oriented to absorb the thrust motion. The thrust bearing also includes a seal dam so that the capacity of the thrust bearing can be increased by additional gas pressure between the rotating and non-rotating bearing surfaces.
This application claims the benefit of U.S. Provisional Application No. 60/560,796 filed Apr. 8, 2004.
The present invention relates to bearings and seals, and more particularly, to pressurized hydrodynamic bearings and seals in which the bearing can be used in both a radial and/or thrust application.
BACKGROUND OF THE INVENTIONTwo types of air bearings are well known in the art. Typically, air bearings are either a metallic foil type bearing or a magnetic bearing. Neither of these bearings requires the use of oil for lubrication although the foil bearing generally has various coatings applied to the foils to provide compliance to the journal. The foil bearing cannot be pressurized to increase bearing load capacity while the magnetic bearing is typically very complex, heavy and expensive.
Another form of non-lubricated, gas film loads support bearing is described in U.S. Pat. No. 5,017,022. In this support bearing, the rotating shaft is formed of a ceramic material such as silicon nitride and the surrounding bearing segments are of a carbon graphite material. The carbon graphite surface is configured with lands and depressions for self generation of a gas film from surrounding hot oxygen bearing gases. The gases are derived from the use of the bearing in a gas turbine engine. However, the film load support is provided at relatively low pressure and this system does not provide a means of increasing the pressure to provide higher bearing load capacities. The system described in the '022 patent was typically useful in the range of about 30 psi for a one inch bearing at a surface speed of approximately 525 feet per second. However, it is desirable to provide a bearing having a significantly larger load capacity such as a capacity in excess of 100 psi.
The graphite ceramic interface used in the '022 patent was further exploited in U.S. Pat. No. 6,322,081 in the development of a circumferential seal for sealing between a rotating shaft and a stationary housing. The seal in the '081 patent comprises a stator mounted to the housing and having a radially inward facing carbon portion and a rotor with a ceramic sealing member having a radially outward facing surface in rubbing contact with a carbon portion. This arrangement of carbon ceramic seal provided a substantially constant engagement between the carbon ring and the ceramic rotor in the presence of varying temperatures. This result is achieved because of the limited deformation of carbon and graphite at varying temperatures.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention is an improvement upon and modification of the bearing described in U.S. Pat. No. 5,017,022, the disclosure of which is hereby incorporated by reference. More particularly, the present invention combines the bearing element concept of the '022 patent with the concept of a carbon ring seal such as that described in U.S. Pat. No. 6,322,081 to create a pressurizable bearing and gain a proportionate increase in bearing load capacity.
In general, air bearing technology usually relates to self-energizing foil type air bearings in which a series of metallic foils and a circumferential array about a cylindrical shaft lift off the shaft during shaft rotation due to the formation of the boundary layer pressure gradient. Such air bearings are limited to load capacity due to foil conformance to the rotating bearing rotor. Non-conformance of the foil to the bearing rotor can interrupt the boundary layer pressure gradient and cause the foil to contact the rotating shaft thereby resulting in excessive frictional heating and bearing failure. Applicant's bearing concept utilizes a single piece or multi-piece segmented stationary bearing member of high density, fine-grained, high temperature, carbon/graphite material with cylindrical and/or radial surfaces that initially contact a rotating bearing journal. The bearing can either be a radial bearing and/or a thrust bearing and can be operated in conjunction with a metallic, ceramic or hybrid ceramic bearing journal.
The rotating bearing member 20 is typically supported on an annular axial retainer 24 and a metallic flex beam 26, both of which elements are well known in the art. Both the elements 24 and 26 are mechanically fixed to the shaft indicated by shaft center line 12. The embodiment of
It can be seen that the embodiment of
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What has been described is an improved bearing/seal arrangement for a high speed rotating shaft in which the bearing is capable of increase loading utilizing high pressure air film to support an outer stationary bearing over an inner rotating bearing surface.
Claims
1. A pressurized hydrodynamic bearing assembly comprising:
- an axially extending rotatable inner member having a smooth surface finish; and
- an outer non-rotating member formed of a carbon/graphite material and adapted to be hydrodynamically supported above a surface of said inner rotating member when the rotational speed of said surface reaches a predetermined value, said outer stationary member including a radially inward extending sealing dam positioned at an axially inner end of said stationary member for preventing leakage of gas from beneath said non-rotating member.
2. The pressurized hydrodynamic bearing assembly of claim 1 wherein the inner rotating member on said rotating shaft comprises a ceramic material.
3. The pressurized hydrodynamic bearing assembly of claim 1 and including a radially outward extending annular bearing segment connected to an axial end of said inner member and another carbon/graphite stationary member positioned in thrust bearing relationship with said bearing segment.
4. The pressurized hydrodynamic bearing assembly of claim 3 and including a seal dam positioned about an outer radial edge of said another stationary member for preventing gas leakage from a space between said bearing segment and said another stationary member.
Type: Application
Filed: Apr 6, 2005
Publication Date: Mar 23, 2006
Inventor: Gary Boyd (Durango, CO)
Application Number: 11/101,172
International Classification: F16C 32/06 (20060101);